A two-year-old can be taught to curb his aggressions completely if the parents employ strong enough methods, but the achievement of such control at an early age may be bought at a price which few parents today would be willing to pay. The slow education for control demands much more parental time and patience at the beginning, but the child who learns control in this way will be the child who acquires healthy self-discipline later.
Selma H. Fraiberg (2015). “The Magic Years: Understanding and Handling the Problems of Early Childhood”, p.155, Simon and Schuster